Field of the Invention
The invention relates generally to osteotomes, and more particularly to surgical methods for expanding an initial osteotomy to receive an implant.
Related Art
An implant is a medical device manufactured to replace a missing biological structure, support a damaged biological structure, or enhance an existing biological structure. Bone implants are implants of the type placed into the bone of a patient. Bone implants may be found throughout the human skeletal system, including dental implants in a jaw bone to replace a lost or damaged tooth, joint implants to replace a damaged joints such as hips and knees, and reinforcement implants installed to repair fractures and remediate other deficiencies, to name but a few. The placement of an implant often requires a preparation into the bone using either hand osteotomes or precision drills with highly regulated speed to prevent burning or pressure necrosis of the bone. After a variable amount of time to allow the bone to grow on to the surface of the implant (or in some cases to a fixture portion of an implant), sufficient healing will enable a patient to start rehabilitation therapy or return to normal use or perhaps the placement of a restoration or other attachment feature.
The present invention is directed toward the preparation of a bone implant in cases where expansion of an initial osteotomy is required. A dental implant is shown in FIG. 1 for exemplary purposes as illustrative of the preparation steps customary in many bone implant applications. According to current techniques, at edentulous (without teeth) jaw sites that need expansion, a pilot hole is bored into the recipient bone to form the initial osteotomy, taking care to avoid the vital structures. The pilot hole is then expanded using progressively wider expander devices called osteotomes, manually advanced by the surgeon (typically between three and seven successive expanding steps, depending on implant width and length). See for example FIG. 2. Once the receiving hole has been properly prepared, a fixture screw (usually self-tapping) is screwed into place at a precise torque so as not to overload the surrounding bone.
The osteotome technique has become widely utilized in situations requiring preparation of an osteotomy site by expansion of a pilot hole. By nature, the osteotome technique is a traumatic procedure. The instruments are advanced with the impact of a surgical mallet, which compacts and expands the bone in the process of preparing osteotomy sites that will allow implant placement. (FIG. 2.) Treatment of a mandibular site, for example, is often limited due to the increased density and reduced plasticity exhibited by the bone in this region. Other non-dental bone implant sites may have similar challenging density and plasticity characteristics. Additionally, since the osteotome is inserted by hammering, the explosive nature of the percussive force provides limited control over the expansion process, which often leads to unintentional displacement or fracture of the labial plate of bone in dental applications. Many patients do not tolerate the osteotome technique well, frequently complaining about the impact from the surgical mallet. In addition, reports have documented the development of a variety of complications that result from the percussive trauma in dental applications, including vertigo and the eyes may show nystagmus (i.e., constant involuntary cyclical movement of the eyeball in any direction).
More recently, a technique has been developed for dental applications that allow the atraumatic preparation of implant sites by eliminating the use of a surgical mallet. This procedure is based on the use of a ridge expansion system that includes a bur kit and instruments known as motor-driven bone expanders, such as those marketed by Meisinger split control bone management system (Neuss, Germany). First a pilot hole is drilled at the implant site, then a series of progressively larger expander screw taps are introduced into the bone by hand or with motor-driven rotation, which decreases surgical trauma (as compared with hammer taps) while providing superior control over the expansion site. See for example FIG. 3. The thread pattern of the expander screw taps has been designed to compact bone laterally as the instrument advances into the osseous crest. This system allows expansion and preparation of implant sites in Type II and III bone, as well as compaction of Type IV bone. The Meisinger split control bone management system may be implemented with a so-called “expander bur” tool to prepare the initial pilot hole to receive the first expander screw tap. In dentistry, the term “bur” is usually synonymous with “cutter.” The expander bur tool apparently grinds a taper on the inner wall of the pilot hole osteotomy that will readily accept the tapered shape of the first expander screw tap.
Since they are operated with an electric hand piece, the expander screw taps can be utilized in the anterior as well as posterior regions without impingement of the facial tissues or the positional limitations imposed by traditional osteotomes (unlike a more traditional mallet-driven osteotome which cannot easily reach for example the lower mandible posterior). Furthermore, the rotational control of the expansion permits treatment of the mandibular atrophic ridge. The system can be utilized by itself or with osteotomes and surgical drills to assist in the placement of a variety of implant design.
US Publication No. 2006/0121415 to Anitua Aldecoa describes the use of motor-driven tools and methods for expanding a human bone for the purpose of installing a dental implant. Similar to the progressive illustration shown in FIG. 3, a starter drill is used to create a pilot hole followed by the insertion of an expander screw tap type osteotome having a conical/cylindrical geometry with progressive cross-section. A surgical motor is used to rotate the osteotome at relatively low speeds. Another example of this technique is described in U.S. Pat. No. 7,241,144 to Nilo et al, issued Jul. 10, 2007. The entire disclosures of US Publication No. 2006/0121415 and U.S. Pat. No. 7,241,144 are hereby incorporated by reference.
In the prior art designs involving motor-driven bone expansion, the rotary speed of the expander screw tap is locked in a fixed relationship to the expansion rate of the osteotomy. This is because the expander tap threads cut into the bone and advance the expander tap deeper into the initial osteotomy with rotation. The “root” of the expander screw tap does the expanding work while vertical advance is controlled by pitch of threads and rotation speed. In other words, the thread pitch of the expander screw tap combined with its taper angle is fixed and cannot be altered by the surgeon. If a surgeon wishes to expand the bone more slowly, the only recourse is to turn the expander more slowly. Conversely, if they wish to expand the bone more rapidly, the only option is to turn the expander tool more quickly. Thus, the rate of bone expansion is a direct and unalterable function of the rate at which the surgeon turns the expander tool, and the surgeon is unable to vary other parameters such as pressure and/or rotation rate to achieve an optimum expansion rate.
The utilization of motor-driven bone expanders served in the past (FIG. 3) as an innovative technique offering an atraumatic alternative to the traditional mallet-driven osteotomes (FIG. 2). These instruments also provide, at least arguably, a favorable increase in the control of the bone expansion, which facilitates implant-site preparation while allowing universal intraoral use. Nevertheless, there are many shortcomings of the present motor-driven bone expander screw tap techniques. These shortcomings include a relatively large number of intermediate progressive expansions steps due to the surgeon's inability to disassociate the tool rotation rate from the bone expansion rate. A typical osteotomy kit for dental applications may include 4-6 expander screw taps which make the kit cost relatively expensive. Another disadvantage is that each expander screw tap takes time to install and perhaps an equal amount of time to remove (i.e., un-screw). Because of the relatively large number of progressive expansions steps needed, this translates to a long surgical procedure which increases patient discomfort and procedure cost. Yet another disadvantage is that each rotary expansion step introduces some degree of error into the osteotomy. In dental applications for example, the surgeon's hand controlling the advancing expander screw tap is typically located outside the patient's mouth, which is laterally offset from the rotational axis of the expander tap. Thus, even though a surgical motor may be used to drive the expander tap, there is a very real possibility that the surgeon will introduce the some tilt or wobble inadvertently as the expander tap is advanced (or withdrawn) thus distorting the intended shape of the osteotomy or even worse provoking a lateral fracture in the bone.
This inexorable linking of tool rotation rate to bone expansion rate in all prior art rotary expander systems limits surgical control over the implant process, and in some cases may lead to unnecessary patient discomfort. There is therefore a need in the art for an improved surgical method for expanding an initial osteotomy to receive an implant in all bone applications, and tools therefor, that provide greater surgical control, are less costly, less likely to introduce error and that reduce patient discomfort.